Carbonated beverages, such as beer, contain carbon dioxide gas which is dissolved in solution. This dissolved carbon dioxide gas affects the flavor profile of the beverage and also causes the characteristic foaming or "outgassing" during dispensing of the beverage.
One type of carbonated beverage dispensing system, typically found, for example, in many bars and restaurants, generally includes a supply container (e.g., a keg) holding a quantity of the beverage. The supply container, in turn is generally attached to a dispensing faucet by a fluid conduit. A supply of pressurized carbon dioxide or nitrogen gas, or a mixture thereof, is typically connected to the supply container in order to maintain the beverage contained within the supply container under pressure. This pressure, in turn, forces the beverage from the supply container through the conduit to the faucet when it is desired to dispense the beverage from the system. Such a dispensing system typically operates at a relatively high pressure, in the range of from about 30 to about 40 psi.
Another type of carbonated beverage dispensing system is a self contained dispensing system. In one type of self contained dispensing system, the beverage is stored within a container and a flexible pressure pouch is immersed within the beverage. The pressure pouch may comprise various compartments housing components of a two-part gas generating system. The pressure pouch may be configured such that, as beverage is dispensed from the system, additional pouch compartments are opened, causing additional chemical components to be mixed. This, in turn, causes the pressure pouch to expand and maintain the pressure within the system. Examples of such self contained dispensing systems, and of pressure pouches used in conjunction therewith, are disclosed in U.S. Pat. No. 4,785,972 to LeFevre; U.S. Pat. No. 4,919,310 to Young et al.; U.S. Pat. No. 4,923,095 to Dorfman et al.; U.S. Pat. No. 5,333,763 to Lane et al.; U.S. Pat. No. 5,769,282 to Lane et al. and U.S. patent application Ser. No. 09/334,737 of Lane et al., filed Jun. 17, 1999, for READILY DEFORMABLE PRESSURE SYSTEM FOR DISPENSING FLUID FROM A CONTAINER, which are all hereby specifically incorporated by reference for all that is disclosed therein.
Some types of beers are commonly charged with nitrogen gas in place of, or in addition to, carbon dioxide gas. Beer that has been charged with nitrogen gas in this manner is commonly referred to as "nitrogenized beer" or, more simply, "nitro beer". In order to properly dispense a nitro beer, it is necessary that the dissolved nitrogen gas be forced out of solution during dispensing, i.e., immediately prior to the time at which the beer is poured into a container or glass to be consumed by a consumer.
Compared to carbon dioxide, nitrogen is relatively difficult to force out of solution. Accordingly, specialized beer taps or faucets may be used for dispensing nitro beers from pressurized dispensing systems. These specialized faucets are specifically designed to agitate the beer in order to force the dissolved nitrogen out of solution. An example of such a specialized faucet for dispensing nitro beer is disclosed, for example, in U.S. patent application Ser. No. 09/362,483 of Whitney et al., filed Jul. 28, 1999, for METHOD AND APPARATUS FOR DISPENSING A LIQUID CONTAINING GAS IN SOLUTION, which is hereby specifically incorporated by reference for all that is disclosed therein.
In conventional (i.e., non nitrogenized) carbonated beverage dispensing systems, however, it is desirable to maintain at least a portion of the carbon dioxide gas in solution to preserve the flavor profile and mouth feel of the beverage. Accordingly, it is desirable to gently reduce the pressure of such a conventional carbonated beverage from the pressure existing within the dispensing system to the ambient atmospheric pressure existing outside of the system. If the pressure is reduced too rapidly, the resulting shock will force a large amount of carbon dioxide out of solution and result in excessive outgassing of carbon dioxide and, thus, an undesirable amount of foaming in the dispensed beverage. Typically, pressure is gently reduced by providing a flow restrictor between the supply of beverage within the system and the exterior of the system. Such a flow restrictor might, for example, comprise a length of tubing through which the beverage is forced to flow. The length and diameter of the tubing are typically chosen so as to provide the proper amount of flow restriction relative to the operating pressure of the dispensing system. Alternatively, such a flow restrictor might take the form of a helical flow path. Examples of flow restrictors for dispensing carbonated beverages are disclosed in U.S. provisional patent application serial No. 60/129,945 of Lane et al., filed Apr. 19, 1999, for METHOD AND APPARATUS FOR DISPENSING A FLUID, which is hereby specifically incorporated by reference for all that is disclosed therein.
The type of flow restrictor described above, however, can be problematic when used in a dispensing system in which the system pressure varies. In the self contained pressure pouch system described above, for example, system pressures may fluctuate significantly, e.g., between about 10 psi and about 25 psi, during operation. This pressure fluctuation is caused by the sequential opening of the pouch compartments and the inability of the two chemical gas generating components to generate gas at a rate that will keep up with the beer dispensing rate. When, for example, a new compartment is opened, additional chemical component will react, eventually causing the pressure to rise. Subsequent dispensing of fluid from the container, on the other hand, will cause the system pressure to decline until another compartment opens.
Such pressure fluctuations make it difficult to select a flow restrictor that functions adequately under all operating conditions. If, for example, a flow restrictor is sized for the average system pressure, then an unacceptably high flow rate (possibly resulting in undesirable foaming) may be experienced when the system is operating toward the higher end of its pressure range. By the same token, an unacceptably low flow rate may be experienced when the system is operating toward the lower end of its pressure range.
Providing a variable flow restrictor for use in conjunction with a fluctuating pressure dispensing system is generally known. This type of variable flow restrictor adjusts the level of flow restriction in response to system pressure in an attempt to maintain a relatively constant dispensing flow rate regardless of system pressure. An example of such a variable flow restrictor for use with a beer dispensing system is disclosed in U.S. Pat. No. 4,210,172 of Fallon et al., which is hereby specifically incorporated by reference for all that is disclosed therein.
This type of variable flow restrictor, however, is relatively expensive and complicated to manufacture. This increased expense and complexity make such variable flow restrictors particularly impractical for use with self contained dispensing systems, which often represent disposable or limited re-use containers.
Accordingly, it would be desirable to provide a dispensing mechanism which provides for the proper dispensing of pressurized beverages and which overcomes the problems discussed above.